Roman.cs

    /// <summary>
    /// Roman
    /// </summary>
    public struct Roman
    {
        /// <summary>
        /// Value
        /// </summary>
        public int Value;

        /// <summary>
        /// Roman
        /// </summary>
        /// <param name="value">Regular Numeral</param>
        public Roman(int value)
        {
            if (value < 0 || value > 3999) throw new ArgumentOutOfRangeException("Value must be between 0 and 3999");
            Value = value;
        }

        /// <summary>
        /// Roman
        /// </summary>
        /// <param name="s">Roman Numeral</param>
        public Roman(string s)
        {
            int value = 0;
            for (int i = 0; i < s.Length; i++)
            {
                if (i + 1 < s.Length && RomanMap[s[i]] < RomanMap[s[i + 1]])
                {
                    value -= RomanMap[s[i]];
                }
                else
                {
                    value += RomanMap[s[i]];
                }
            }
            if (value < 0 || value > 3999) throw new ArgumentOutOfRangeException("Value must be between 0 and 3999");
            Value = value;
        }

        /// <summary>
        /// To String
        /// </summary>
        /// <returns>Roman Numeral</returns>
        public override string ToString()
        {
            int value = Value;
            StringBuilder s = new StringBuilder();
            foreach (var item in NumberMap)
            {
                while (value >= item.Key)
                {
                    s.Append(item.Value);
                    value -= item.Key;
                }
            }
            return s.ToString();
        }

        private static readonly Dictionary<char, int> RomanMap = new Dictionary<char, int>()
        {
            {'I', 1},
            {'V', 5},
            {'X', 10},
            {'L', 50},
            {'C', 100},
            {'D', 500},
            {'M', 1000}
        };

        private static readonly Dictionary<int, string> NumberMap = new Dictionary<int, string>()
        {
            { 1000, "M" },
            { 900, "CM" },
            { 500, "D" },
            { 400, "CD" },
            { 100, "C" },
            { 90, "XC" },
            { 50, "L" },
            { 40, "XL" },
            { 10, "X" },
            { 9, "IX" },
            { 5, "V" },
            { 4, "IV" },
            { 1, "I" },
        };
    }